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I'm a newbie at networking. I understand the concept of multicast, but was wondering if it's reliable on the open/public internet?
It seems like sort of an edge case that different backbones or ISPs might intentionally break to reduce router load or generally segment the network for practical high-use applications.
Is my fear reasonable?
P.S. Follow-up question here: Best tutorial for application multicasting?
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IP Multicast A source sends a packet destined for a group of other hosts and the intermediate routers take care of replicating the packet as necessary. The intermediate routers are also responsible for determining which hosts are members of the group. IP Multicast uses UDP for communication, therefore it is unreliable.
Security concerns in IP multicast: Multicast security is more difficult than unicast security in several areas. There are some special problems with the secure multicast that won't arise with unicast and many security aspects that are not apparent in unicast are clear and should be resolved in IP multicast.
Drawbacks of multicastingAs more users connect to the network, the bandwidth available for each user decreases, so multicast technology can become inefficient. For example, a single video stream may efficiently transmit data to all the clients that need it, but one device may have less bandwidth than others.
Many networks, including the Internet, do not support multicast routing. Multicast routing functionality is available in enterprise-grade network equipment but is typically not available until configured by a network administrator. The Internet Group Management Protocol is used to control IP multicast delivery.
IP multicast in the internet doesn't really work. From the Wikipedia article:
For both these reasons, and also reasons of economics, IP Multicast is not in general use in the commercial Internet.
People who desire to participate in the global IP multicast need to attach themselves to the MBONE. The Wikipedia article points out that application-level multicast infrastructures do work, e.g. IRC.
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Yeah, internet-scale multicast routing isn't really a solved problem, nor is there much progress from what I can tell.
The current recommended large scale solution is source-specific multicast, SSM, whereby as a client to request multicast traffic from specific sources rather than wide open listening. This still requires support from all intermediary routers and so may only become more practical with IPv6 which mandates multicast support as opposed to IPv4 which it is optional and frequently disabled.
http://en.wikipedia.org/wiki/Source-specific_multicast
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Yeah, internet-scale multicast routing isn't really a solved problem, nor is there much progress from what I can tell.
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